Although the underlying mechanisms of fatigue have been studied in several disease conditions, the etiology, mechanisms, and risk factors remain elusive, and this symptom remains poorly managed at present. Longitudinal studies related to treatment-related fatigue in cancer patients have been conducted, but there are limited data showing changes in molecular mechanisms before and after cancer therapy which can identify individuals who are at risk to experience fatigue during and after therapy. Fatigue is conceptualized as a multidimensional symptom which incorporates temporal, sensory, cognitive/mental, affective/emotional, behavioral, and physiological dimensions. This prospective, observational study will explore the molecular-genetic mechanisms underlying fatigue experienced by cancer patients receiving various therapies (e.g. immune therapy, hormone therapy, and chemotherapy). The primary objective of the study is to describe the changes in the self-reported fatigue, depression, and health-related quality of life (HRQOL) experienced by cancer patients before, during, and after cancer therapy. The secondary objectives of this study are to investigate the pro-inflammatory cytokine profile (TNF, IGF-I, IL-6, IL-8, TGF and ), determine changes in gene expression from peripheral blood and tissue samples before, during, and after cancer treatment and to relate changes in the levels of these biological markers to self-reported fatigue, depression, and HRQOL scores. This study also aims to measure the skeletal muscle strength, cognitive function, activity levels and energy expenditure of patients before, during, and at completion of cancer treatment and relate these findings with self-reported fatigue, depression, and HRQOL scores.